1. Field of the Invention
The present invention relates to a method and to a member for tightening one or more screw-fastener elements, and also to a fastener and tightening device enabling the method to be performed.
2. Brief Description of the Related Art
Controlling the tightening of a screw-fastener element, such as a nut, a bolt, or a stud, conventionally relies on determining the tightening torque to be applied to the screw-fastener element. In the usual approach, applying this tightening torque requires a calibrated tightening member to be used, and also requires the tightening torque for application to be determined. This determination may be performed on the basis of the coefficient of friction between the threads, which is data provided by the screw-fastener manufacturer. Such tightening to torque therefore requires action to be performed by a qualified operator.
It is also known to make use of standardized tightening means for transmitting a predetermined tightening toque to a screw-fastener element, said means being designed to transmit destructive forces to the screw-fastener element when the predetermined torque is reached. In such devices, once the screw-fastener element has been tightened, it is damaged and cannot be tightened again in the event of variations in the tightening, as might result for example from vibration or creep of the material on which the screw-fastener element is mounted, when the material is concrete or wood.
U.S. Pat. No. 3,425,314 discloses a fastener and tightening device that comprises a nut and a ring for turning said nut. The ring is constituted by a succession of tubular portions that are separated in pairs by slits. When the tightening torque between the ring and the nut reaches a maximum value, the above-mentioned portions flex outwards under the action of a ratchet defined externally by the nut. Thus, the operation of that device relies solely on the capacity of portions of its ring to flex, thus preventing the delivery of a high level of tightening force and preventing an accurate transmission of force to the vertices of the ratchet, which are entirely unsuitable for implementing tight-fit interference.
U.S. Pat. No. 4,176,582 and FR-A-2 791 404 disclose fastener and tightening devices including a member for turning a screw-fastener element. That member is designed to transmit limited torque because its material is capable of deforming easily. Similarly, U.S. Pat. No. 6,364,585 discloses a tightening member described as being a resin endpiece, that is suitable for deforming elastically in its material so as to transmit a torque of limited magnitude to a screw-fastener element. Thus, the devices proposed in those documents are structurally incapable of delivering a high level of tightening or of transmitting an accurate force.